Ruggedized electron tube



y 1960 P. A. DE BACKER 2,937,305

RUGGEDIZED ELECTRON TUBE Filed June 26, 1958 1 I :z I I 11 i I. u

INVENTOR. L umzn PA. Dr: BHEKER BY jaw cathode.

2,931,305 RUGGEDIZED ELECTRON TUBE Lucien P. A. De Backer, Bloomfield,NJ., assignor to Radio Corporation of America, a corporation of DelawareApplication June 26, 1958-, Serial No. 744,831

1 Claims. (Cl; 313-247).

This invention relates to electron tubes, and particularly to anelectron tube having a relatively rugged structure for preserving aprees'tablished spacing between a cathode and a grid.

One type of electron tube in which the invention finds particularutility is the so-called pencil tube. A pencil tube comprises astructure including an elongated envelope having metallic end portionsand an intermediate portion made of insulating material such as glass orceramic. A metallic disc having a central opening is sealed across theintermediate portion. I

In a triode type of pencil tube, 'a tubular grid is sup ported on themetallic disc with an end portion of the grid extending through theopening in the disc and fixed to the walls defining the opening. Thegrid thus extends towards one end portion of the envlope. 'A tubularanode is supported in the aforementioned end portion and surrounds thegrid in concentric relation therewith. A tubular cathode is supported inthe other'envelope end portion and extends intothe grid in concentricrelation therewith.

It will be seen from the foregoing that the three tubular electrodes aresupported at one end portion thereof, with the other end portion free ofsupport. In this situation, there is likelihood of vibration of the freeend portions when the tube is subjected to impacts. Such vibrationproduces adverse effects, such as microphonics in the cut put of asystem in which the tube is used.

In the structure aforementioned the anode is relatively massive andextends only slightly from its supported region. Therefore the anode iselfectively restrained from a vibrational response to impacts. However,the

- free ends of the grid and cathode extend an appreciable distance fromtheir regions of support and are relatively light in structure.Suchlight structure, while reducing the burden imposed on the supportelements, such as the disc and an end portion of the envelope, isincapable of providing adequate support for the free end portions ofthese electrodes in certain circumstances. (For example, when the gridand cathode are extremely closely spaced in ultra high frequencyapplications involving impacts of appreciable magnitude, the free endportions of these electrodes may respond to the impacts in vibrationshaving an amplitude suflicient to bridge the spacing between .theelectrodes.

In attempting to meet the foregoing problem, it .has been foundimpractical to utilize the anode in a'support system. This is becausethe anode is usually operated at a relatively high voltage differencewith respect to the grid and cathode. Consequently, an insulatingsupport utilizing both the anode and the free end portions of the gridand cathode would give rise to current leakage between the anode and oneor both of the grid and It is therefore an object of the invention tosupport the free end portions of a tubular grid and cathode in a penciltype tube.

. Afurther object is to support ruggedly free end por- 2,937,305Patented May 17, 1960 ICE tions of two relatively closely spacedelectrodes by a support element disposed between the electrodes andhaving a larger transverse extent than the normal spacing between theelectrodes.

An embodiment of the invention, selected for illustrative purposes, andin which the foregoing objects and purpose are realized, comprises apencil type tube wherein a tubular cathode and grid are supported at oneend portion only, and free end portions of these electrodes extend intelescoped relation into a tubular anode. For supporting the free endportions of the grid and cathode, a ring shaped support member which maybe made of a ceramic, is snugly interposed between the cathode and gridfree end portions. However, since the normal spacing between the cathodeand grid may beso small as to render the use of such spacing memberimpractical, pro- ;vision is made, according to the invention,for'enlarging 'the spacing between the cathode and grid free endportions referred .to, without modifying the spacing between the gridfree end portion and the anode. To this end, the free end portion of thecathode is reduced in transverse extent to a value smaller than that of.the active portion of the cathode. extent results in desiredenlargement of the annular space between the free end portions of thecathode and grid, and permits utilization of a support member ofconvenient handling size. p

This manner of engagement of the free end portions of the cathode andgrid provides a relatively rugged support of such free end portions.Appreciably contributing to such ruggedness is the axial displacement ofthe supported ends of the enode and cathode. This displacement resultsfrom the fact that the disc to which the grid is supported, is closer tothe free end portions of the cathode and grid, than the envelope endportion to which the cathode is supported. Consequently, vibration ofthe free end portion of the cathode will occur through' arcs of longerradius than vibrations of the free end portion of the grid. When bothend portions vibrate simulintroduces a component of motion axially ofthese electrodes. However, theinsulating member snugly engaging the freeend portions of the cathode and anode contributes to a restraint of theaforementioned component of motion.

Such restraint of axial movement, is in addition to the damping effectproduced by resistance to bending of the portions of the cathode andgrid engaged by the support member aforementioned. Any vibration of thefree end portions of the cathode and grid would involve a bendingthereof at the region engaged by the support member. This is because thecathode and grid would extendalong angular-1y disposed axis duringperiods of vibration,- and the support member would be incapable ofpreserving a coaxial relation with each of the angularly disposedcathode and grid referred to. However, the material stiffness of thecathode and grid resist the bending thereof required for vibration, andhence contributes to a restraint of vibration.

In addition to the foregoing restraints to vibration of the free endportions of the cathode and grid, impedance Such reduction intransversethe cathode and grid. This is particularly significant in atube of the type referred to, since in such tube the characteristicsthereof are appreciably more dependent on the cathode-grid spacing, thanthe anode-grid spacing. One reason for this is that in most applicationsthe anode-grid spacing is many times as great as the cathodegridspacing, so that a given change in spacing is relatively much greaterwhen it concerns the grid and cathode, than when it relates to the gridand anode.

It will be seen from the foregoing, therefore, that incorporation of theinvention in a tube structure is accompanied by many advantages.

Further features and purposes of the invention will become apparent asthe instant description proceeds.

Reference to the accompanying drawing for a more detailed considerationof an embodiment of the inven tion will reveal that I Fig. 1 shows alongitudinal crossrsection of an electron tube in which the invention isembodied;

Fig. 2 shows a transverse section along the lines 272 of Fig. l; and

Fig. 3 is a fragmentary sectional view of a tube showing a modifiedembodiment of the invention.

The electron tube shown in Fig. 1 is of the pencil type and includes anenvelope formed by two metallic end portions 12 and an intermediateportion formed by tubular members 14, 16 which may be made of glass or aceramic. Tubular member 14 is sealed to a flange 18 extending from endportion 10, and tubular member 16 is sealed to a similar flange 20extending from end portion 12. Adjacent ends of tubular members 1 16 aresealed to a metal disc 22 by means of brackets 2-4.. The disc 22 isprovided with a central opening 26 defined by walls including acylindrical portion 28 and a beveled portion 30.

In end portion 10, an anode 32 is supported and is fixed by means of aforce fit relation with respect to the end portion, or by being brazedthereto. A cathode support 34 is fixedly positioned in end portion 12 asby a force fit or by brazing. A tubular cathode 36 may be fixed tosupport 34, in a suitable way as by welding or brazing, either directlyor through an intermediate tubular portion of reduced heat conductivitymade of a material such as Kovar. A grid 37 of tubular shape is mountedat one end thereof on disc 22, by engaging the wall portions 28,defining the opening 26 through the disc.

End portions 10 and 12 are closed by a pinched exhaust tubulation 38 anda wafer 40 of insulating material, respectively, to preserve a desiredvacuum condition with the envelope referred to. Lead-ins 42, 44 areconnected to. a heater 45 within the cathode 36.

It will be noted that the aforedescribed mounting of the electrodes,disposes an active portion of the anode 32 partly in end portion 10 andpartly in the space between this; end portion and the disc 22. The anodeextends a relatively short distance from its region of engagement by endportion 10, and is relatively massive, so that the free end portionthereof is restrained effectually from vibration.

The mounting arrangement described also disposes grid 37 partly in endportion 10 and fully along the space between this end portion and thedisc 22. The grid 37, therefore, extends a greater distance from itssupport than the anode 32. This greater distance, coupled with therelatively light structure of the grid, as will appear more fully in thefollowing, render the free end portion of the grid more responsive invibration to shocks applied to the tube, than the anode aforementioned.

With respect to the mounting of the cathode 36, it will be noted thatone end thereof is fixed to support 34 in a region spaced farther fromthe anode 32 than the grid supporting disc 22. Consequently, when thecathode is provided with a length so that its free end coincidessubstantially with the free end of grid 37, such free cathodeendisfarther spaced from the region of cathode support than characterizes thespacing between the free end of grid 37 and its support. However, whilethe cathode has a greater length from its free end to its support, it isinherently stronger than the grid because of its imperforate character.Therefore, the free end of the cathode is less responsive in vibrationto tube shocks than the free end of the grid.

While the anode 32 is relatively massive and is ruggedly supported, ithas not been found practical to support the free end portionsv of thecathode 36 and grid 37 thereon. This is because such support willinvolve the use of an insulating member engaging the anode and one orboth of the grid and cathode. Such engagement would be objectionable inthat it would lead to current leakage across the insulatingmember, inview of the relatively high voltage difference between the anode on theone hand and the grid and cathode on the other, usually req red d r opation o h tube.- 7

c r ng e t e i ent o t e prob m of v bratie of the. free end portions ofthe grid 37 and, cathode 3.6 is met, by interposing an insulating ringshapedmember 46, between the free end portions of the cathode and grid.For enlarging the space between the end portions referred to, thecathode 36 is preferably of reduced diameter at its free end portion, asshown at 48 (Fig. 1;). This permits use of an insulating member 46 ofdesired size for convenient handling. In addition, the reduction in thetransverse extent of the cathode free end portion provides a longerleakage path from the cathode to the grid, and reduces the area ofengagement between the cathode and the insulating member 46, to reduceheat drain from the cathode. While the voltage difference. between thecathode and grid in operation of a tube of the type referred to isrelatively small, the tolerable spacing between the cathode andv grid isso smalL that some current leakage is likely between the two, across aspacing member therebetween, if the spacing member bridges therelatively small normal spacing between the cathode and grid.

The insulating member 46 may be made of a ceramic such as. aluminumoxide and has an outer diameterfor snugly engaging the inner wall of thefree end portion of grid 37. For convenience in practicing a methodfeature of the invention to be described, the grid 37 may have astructure comprising'a plurality of parallel side rods 50 disposed in acircular array (Fig. 2) and turns of lateral wires 52 fixed to the outersides of the side rods in the aforementioned array. In this way theinner sides of the side, rods will provide tracks along which the snuglyfitting insulating member may be slidingly moved to the free end portionof the grid. However, a grid having the laterals on the inner sides ofthe side rods may be used provided the grid turns are spaced to a lesserdegree than the thickness of the insulating member 46.

Before the insulating member 46 is positioned in the grid 37, it isfirst fixed to the turned-down end portion 48 of the cathode. The fixingis accomplished by a tight fit of the insulating member around thecathode end portion, and by an outward flare 53 in the cathode end. Theturned down cathode portion 48 is of such length that the insulatingmember 46 is wedged between a shoulder 54 on the cathode and theaforementioned fiare53.

In practicing the method aspects of the invention, the grid 37 is fixedas by welding to disc 22, with an end portion of the grid engaging thewall portions 28, 30, defining opening 26 through the disc. Thereafteran assembly comprising support 34, cathode 36 and insulating member 46fixed as aforedescribed to the turned-down free end portion 48 of thecathode, is extended first through the open end portion 12, with thecathode leading. Continued extending'movement of the assembly causes theinsulating member 46 on the leading end of the cathode to be guided intogrid 37 by the bevelled wall por-. t-ion 2'6of the disc 22. This permitstheinsulatingmemher to enter the grid even though the member fitsrelatively tightly in the grid. Further'extension of the assembly causesthe insulating member 46 to slide on the inner side of side rods 50 ofthe grid to a position in engagement with the free end portion of thegrid. At the same time cathode support 34 is moved to a predeterminedposition, in which it is fixed, as by brazing, to the inner wall of endportion 12, for completion of the mounting operation.

Instead of turning down a portion of the cathode to provide the free endportion 48 (Fig. l) the cathode may comprise a sleeve 56 (Fig. 3) towhich is fixed as by brazing or welding a relatively small tube 5-8 ofsmaller diameter than the cathode. The end portion of the cathodeengaging the tube 58 is preferably turned in as at 60 to provide aflange meeting a flange 62 on the tube 58. The cathode end portionreferred to defines an opening 64 to provide communication between theinterior of the cathode and the tube envelope for the purpose ofevacuation. Insulating member 46 is fixed to tube 58 by being wedgedbetween flange 62 at one end of the tube, and an outward flare 66 in theother end of the tube.

A cathode assembly including the tube 58, insulating member 46 andcathode support 34, may be mounted in relation to grid 37, in the sameway as the cathode assembly including cathode end portion 48, aspreviously described.

I claim:

1. An electron tube having first and second elongated tubularelectrodes, said electrodes being disposed in telescoped relation withone group of adjacent ends terminating substantially in common plane,said electrodes having another group of adjacent ends spaced axially ofthe electrodes, support means adjacent to said another group of endsfixedly engaging said last named ends, an envelope for said tube, saidsupport means being fixed to said envelope, and means engaging said onegroup of adjacent ends only, for restraining relative movement of saidends, said means being disposed solely between said one group of endsand constituting the sole support for said ends, one of said one groupof ends being deformed to enlarge the transverse dimension of theannular space between said one group of ends, said last named meanscomprising a spacing member disposed solely in said space.

2. An electron tube having an envelope, two parallel elongatedelectrodes within said envelope, one group of adjacent ends of saidelectrodes lying in spaced planes normal to said electrodes, the othergroup of adjacent ends lying substantially in a common plane, meansfixedly supporting said one group of ends, with respect to saidenvelope, and a spacer member engaging said electrodes only, adjacentsaid other group of ends thereof for restraining relative movement ofsaid last named ends, said electrodes being spaced a normalpredetermined distance from each other, said other group of ends beingspaced from each other a distance greater than said predetermineddistance, whereby a relatively large annular space is provided betweensaid last named ends, said spacing member being disposed only in saidspace only and constituting the sole support for said last-named ends.

3. An electron tube having an elongated envelope, two electrodes withinsaid envelope and parallel to the axis thereof, one of said electrodeshaving an end portion fixed to one end portion of said envelope, theother of said electrodes having an end portion fixed to an intermediateportion of said envelope, said electrodes having active portionsmutually spaced a predetermined distance, said electrodes having otherand adjacent end portions, said adjacent end portions being mutuallyspaced :1 distance greater than said predetermined distance, and aninsulating member engaging and disposed only between said adjacent endportions and constituting the sole support therefor, for restrainingrelative movement of said last named end portions.

4. An electron tube having an elongated envelope, a tubular anodesupported in one end portion of said en- 6 velope and extending towardsan intermediate portion of said envelope, a tubular grid having one endportion supported at said intermediate portion and another end portionextending into said anode, a tubular cathode supported at one endportion thereof in the other end portion of said envelope and extendinginto said grid end portion, said cathode having an active portion withinsaid grid spaced a predetermined distance from the inner wall of thegrid, and an end portion adjacent the other end thereof spaced from saidinner wall a distance whereby an annular space is provided between saidend portion and said grid, greater than said predetermined distance,

and an insulating member engaging said inner Wall and the outer wall ofsaid cathode end portion and free from contact with said anode andconstituting the sole support for said other end of said cathode andsaid another end portion of said grid, for restraining movement of saidcathode and grid with respect to said anode, said insulating memberconsisting of an annular structure disposed entirely within said annularspace.

5. An electron tube having an elongated envelope, a tubular anodesupported in one end portion of said envelope and extending towards anintermediate portion of the envelope, a tubular grid having one endsupported on said intermediate envelope portion and having another endin a predetermined plane Within said anode, a tubular cathode having oneend supported in the other end portion of said envelope and another endsubstantially in said predetermined plane and within said grid, saidcathode including a portion adjacent to said another end thereof ofsmaller transverse extent than other portions thereof, and an insulatingmember engaging only the outer wall of said cathode portion and theinner wall of said grid adjacent to said another end thereof, forrestraining movement of said cathode and grid with respect to saidanode, said insulating member constituting the sole support for saidanother end of said cathode and said another end of said grid.

6. In an electron tube, a mount comprising a. support, a tubular gridsupported at one end on sad support, a tubular cathode supported at oneend on said support and extending into said grid, said grid and cathodehaving adjacent end portions remote from said support, said end portionof said cathode being of smaller tranverse extent than other portions ofthe cathode for enlarging the transverse dimension of the annular spacebetween said grid and cathode end portions, and an insulating memberdisposed solely in said annular space and engaging said grid and cathodeend portions for restraining relative movement therebetween, saidinsulating member constituting the sole support for said adjacent endportions.

7. A cathode subassembly for an electron tube comprising a tubularmember having opposite end portions of different transverse extents andan intermediate active portion of a transverse extent intermediate saiddifierent transverse extents, and an insulating member fixed to andengaging sides only, of the end portion of smaller transverse extent andhaving a transverse extent intermediate the transverse extents of theother of said end portions and said intermediate portion, whereby saidother of said end portions is adapted to engage a support for ruggedlysupporting said other end portion of said tubular member, and saidinsulating member is adapted to engage another electrode of said tubefor simultaneously spacing and supporting said end portion of smallertransverse extent with respect to said other electrode.

References Cited in the file of this patent UNITED STATES PATENTS1,989,819 Parrott Feb. 5, 1935 2,473,969 Pryslak et al June 21, 19492,828,438 McArthur Mar. 25, 1958 2,849,639 Fehr et a1 Aug. 26, 19582,866,120 Morris et a1. Dec. 23, 19 58

